The present invention relates to a control apparatus for an electric fuel pump adapted for use with engines for vehicles such as automotive vehicles.
In conventional vehicle engines, generally the fuel stored in a fuel tank is supplied by a fuel pump to each fuel injection valve or the float chamber of a carburetor. The fuel is then supplied to the intake system of the engine by the fuel injection valve or the carburetor.
Fuel pumps of the type operated by an electric motor are known in the art, and Japanese Laid-Open Patent Application No. 58-48767 discloses an apparatus for controlling the operation of an engine electric fuel pump as a countermeasure for suppressing the noise caused by the fuel pump during the idling, low load operation or low speed operation of the engine. This control apparatus is designed so that in accordance with the engine operating conditions, e.g., the cooling water temperature, rotation speed and intake air flow of the engine, the applied voltage of the fuel pump operating motor is varied so as to control its rotation speed in accordance with the required fuel delivery of the fuel pump, which varies with the operating conditions of the engine, thereby reducing the fuel pump noise.
However, the control apparatus disclosed in the above-mentioned application is disadvantageous in that since the applied voltage of the fuel pump operating motor is varied in accordance with the operating conditions of the engine, even under the same operating conditions, if the battery is more or less tending to discharge so that the battery voltage is decreased, the applied voltage of the fuel pump operating motor is also decreased, and the rotation speed of the motor is decreased thus decreasing the amount of fuel delivered by the fuel pump. Then, in the worst case, there is the danger of a situation arising in which even the fuel quantity to be consumed by the engine cannot be supplied.